Your post is intriguing: If their cost of living is more expensive than the US AND their earning is lower, how do they manage to have a great quality of life? Of course I'm only comparing comparable cities (I'm not comparing NYC to a rural village in Europe, for example).
About student debts, I find that most EU universities cost little to nothing (if anything, they cost up to $1000/year - except the UK, which is almost as expensive as the US)...
Taxes, and all the government-paid benefits that those bring (Scandinavian countries are the perfect examples of "welfare states"). As a whole, many European societies have decided to distribute their wealth around much more equally. There are obviously pros and cons to this.
In general, if you are lazy, you will have a better qualify of life in socialist European countries. But if you're hard working there's little incentive to work hard and accumulate wealth only to fork most over to the government/everyone else, which is why people with a more entrepreneurial spirit will have a better quality of life in the US (maybe not better qualify of life necessarily, but more money and in theory a better opportunity for a better quality of life). It's all relative--I don't think either system is inherently better--some are better for certain populations (Scandinavia is very homogenous--and they will admit quite boring...) and others better for other populations.
The issue is some European countries go a little too far and essentially incentivize laziness. Greece would be a prime example--sure, they had a great quality of life, but is it sustainable? I don't think the younger generation in Greece will have much quality of life burdened by all the debt of their parents/grandparents. The US maybe goes too far in the other direction--we all know how unequal society here is.
Personally, I don't see the point of accumulating massive amounts of wealth. I think the goal in life is to learn to be happy with what you have, and make your society better. I think Europeans generally have the better mindset when it comes to their focus on enjoying life. Earn enough to live on and have your needs and most of your wants met, and you'll be happy. If the same can be said for most of your countrymen, then you have a rather pleasant and "rich" society, in my opinion. Making that concept sustainable is pretty tough--without the oil wealth I doubt Scandinavia could do it.
I think if you mix the American mentality of hard work (which isn't quite the same mentality as it was in the past--but it's still better than in most other countries) with the European focus on quality of life and not just accumulation of wealth, you'd get quite a nice society. Maybe it wouldn't be a world power, but it'd be one where most people are quite happy with their lives and feel like their hard work still pays off, but that there's a better safety net for those who need it (obviously a delicate and debatable topic...)
Maybe Canada, eh?